Comparison of hypoxia-activated prodrug evofosfamide (TH-302) and ifosfamide in preclinical non-small cell lung cancer models

Hypoxia-activated prodrug and antiangiogenic therapies cooperatively treat pancreatic cancer but elicit immunosuppressive G-MDSC infiltration

We previously showed that ablation of tumor hypoxia can sensitize tumors to immune checkpoint blockade (ICB). Here, we used a Kras+/G12D TP53+/R172H Pdx1-Cre-derived (KPC-derived) model of pancreatic adenocarcinoma to examine the tumor response and adaptive resistance mechanisms involved in response to 2 established methods of hypoxia-reducing therapy: the hypoxia-activated prodrug TH-302 and vascular endothelial growth factor receptor 2 (VEGFR-2) blockade. The combination of both modalities normalized tumor vasculature, increased DNA damage and cell death, and delayed tumor growth. In contrast with prior cancer models, the combination did not alleviate overall tissue hypoxia or sensitize these KPC tumors to ICB therapy despite qualitative improvements to the CD8+ T cell response. Bulk tumor RNA sequencing, flow cytometry, and adoptive myeloid cell transfer suggested that treated tumor cells increased their capacity to recruit granulocytic myeloid-derived suppressor cells (G-MDSCs) through CCL9 secretion. Blockade of the CCL9/CCR1 axis could limit G-MDSC migration, and depletion of Ly6G-positive cells could sensitize tumors to the combination of TH-302, anti-VEGFR-2, and ICB. Together, these data suggest that pancreatic tumors modulate G-MDSC migration as an adaptive response to vascular normalization and that these immunosuppressive myeloid cells act in a setting of persistent hypoxia to maintain adaptive immune resistance.

Targeting Hypoxia: Hypoxia-Activated Prodrugs in Cancer Therapy

Hypoxia is an important characteristic of most solid malignancies, and is closely related to tumor prognosis and therapeutic resistance. Hypoxia is one of the most important factors associated with resistance to conventional radiotherapy and chemotherapy. Therapies targeting tumor hypoxia have attracted considerable attention. Hypoxia-activated prodrugs (HAPs) are bioreductive drugs that are selectively activated under hypoxic conditions and that can accurately target the hypoxic regions of solid tumors. Both single-agent and combined use with other drugs have shown promising antitumor effects. In this review, we discuss the mechanism of action and the current preclinical and clinical progress of several of the most widely used HAPs, summarize their existing problems and shortcomings, and discuss future research prospects.

The Hypoxia-Activated Prodrug TH-302: Exploiting Hypoxia in Cancer Therapy

Hypoxia is an important feature of most solid tumors, conferring resistance to radiation and many forms of chemotherapy. However, it is possible to exploit the presence of tumor hypoxia with hypoxia-activated prodrugs (HAPs), agents that in low oxygen conditions undergo bioreduction to yield cytotoxic metabolites. Although many such agents have been developed, we will focus here on TH-302. TH-302 has been extensively studied, and we discuss its mechanism of action, as well as its efficacy in preclinical and clinical studies, with the aim of identifying future research directions.

Combining hypoxia-activated prodrugs and radiotherapy in silico: Impact of treatment scheduling and the intra-tumoural oxygen landscape

Hypoxia-activated prodrugs (HAPs) present a conceptually elegant approach to not only overcome, but better yet, exploit intra-tumoural hypoxia. Despite being successful in vitro and in vivo, HAPs are yet to achieve successful results in clinical settings. It has been hypothesised that this lack of clinical success can, in part, be explained by the insufficiently stringent clinical screening selection of determining which tumours are suitable for HAP treatments. Taking a mathematical modelling approach, we investigate how tumour properties and HAP-radiation scheduling influence treatment outcomes in simulated tumours. The following key results are demonstrated in silico: (i) HAP and ionising radiation (IR) monotherapies may attack tumours in dissimilar, and complementary, ways. (ii) HAP-IR scheduling may impact treatment efficacy. (iii) HAPs may function as IR treatment intensifiers. (iv) The spatio-temporal intra-tumoural oxygen landscape may impact HAP efficacy. Our in silico framework is based on an on-lattice, hybrid, multiscale cellular automaton spanning three spatial dimensions. The mathematical model for tumour spheroid growth is parameterised by multicellular tumour spheroid (MCTS) data.

Blackboard to Bedside: A Mathematical Modeling Bottom-Up Approach Toward Personalized Cancer Treatments

Cancers present with high variability across patients and tumors; thus, cancer care, in terms of disease prevention, detection, and control, can highly benefit from a personalized approach. For a comprehensive personalized oncology practice, this personalization should ideally consider data gathered from various information levels, which range from the macroscale population level down to the microscale tumor level, without omission of the central patient level. Appropriate data mined from each of these levels can significantly contribute in devising personalized treatment plans tailored to the individual patient and tumor. Mathematical models of solid tumors, combined with patient-specific tumor profiles, present a unique opportunity to personalize cancer treatments after detection using a bottom-up approach. Here, we discuss how information harvested from mathematical models and from corresponding in silico experiments can be implemented in preclinical and clinical applications. To conceptually illustrate the power of these models, one such model is presented, and various pertinent tumor and treatment scenarios are demonstrated in silico. The presented model, specifically a multiscale, hybrid cellular automaton, has been fully validated in vitro using multiple cell-line-specific data. We discuss various insights provided by this model and other models like it and their role in designing predictive tools that are both patient, and tumor specific. After refinement and parametrization with appropriate data, such in silico tools have the potential to be used in a clinical setting to aid in treatment protocols and decision making.

An Intratumor Pharmacokinetic/Pharmacodynamic Model for the Hypoxia-Activated Prodrug Evofosfamide (TH-302): Monotherapy Activity is Not Dependent on a Bystander Effect

Tumor hypoxia contributes to resistance to anticancer therapies. Hypoxia-activated prodrugs (HAPs) selectively target hypoxic cells and their activity can extend to well-oxygenated areas of tumors via diffusion of active metabolites. This type of bystander effect has been suggested to be responsible for the single agent activity of the clinical-stage HAP evofosfamide (TH-302) but direct evidence is lacking. To dissect the contribution of bystander effects to TH-302 activity, we implemented a Green's function pharmacokinetic (PK) model to simulate the spatial distribution of O₂, TH-302 and its cytotoxic metabolites, bromo-isophosphoramide mustard (Br-IPM) and its dichloro derivative isophosphoramide mustard (IPM), in two digitized tumor microvascular networks. The model was parameterized from literature and experimentally, including measurement of diffusion coefficients of TH-302 and its metabolites in multicellular layer cultures. The latter studies demonstrate that Br-IPM and IPM cannot diffuse significantly from the cells in which they are generated, although evidence was obtained for diffusion of the hydroxylamine metabolite of TH-302. The spatially resolved PK model was linked to a pharmacodynamic (PD) model that describes cell killing probability at each point in the tumor microregion as a function of Br-IPM and IPM exposure. The resulting PK/PD model accurately predicted previously reported monotherapy activity of TH-302 in H460 tumors, without invoking a bystander effect, demonstrating that the notable single agent activity of TH-302 in tumors can be accounted for by significant bioreductive activation of TH-302 even in oxic regions, driven by the high plasma concentrations achievable with this well-tolerated prodrug.

Administration of Hypoxia-Activated Prodrug Evofosfamide after Conventional Adjuvant Therapy Enhances Therapeutic Outcome and Targets Cancer-Initiating Cells in Preclinical Models of Colorectal Cancer

Purpose: Cancer-initiating cells (C-IC) have been described in multiple cancer types, including colorectal cancer. C-ICs are defined by their capacity to self-renew, thereby driving tumor growth. C-ICs were initially thought to be static entities; however, recent studies have determined these cells to be dynamic and influenced by microenvironmental cues such as hypoxia. If hypoxia drives the formation of C-ICs, then therapeutic targeting of hypoxia could represent a novel means to target C-ICs.Experimental Design: Patient-derived colorectal cancer xenografts were treated with evofosfamide, a hypoxia-activated prodrug (HAP), in combination with 5-fluorouracil (5-FU) or chemoradiotherapy (5-FU and radiation; CRT). Treatment groups included both concurrent and sequential dosing regimens. Effects on the colorectal cancer-initiating cell (CC-IC) fraction were assessed by serial passage in vivo limiting dilution assays. FAZA-PET imaging was utilized as a noninvasive method to assess intratumoral hypoxia.Results: Hypoxia was sufficient to drive the formation of CC-ICs and colorectal cancer cells surviving conventional therapy were more hypoxic and C-IC-like. Using a novel approach to combination therapy, we show that sequential treatment with 5-FU or CRT followed by evofosfamide not only inhibits tumor growth of xenografts compared with 5-FU or CRT alone, but also significantly decreases the CC-IC fraction. Furthermore, noninvasive FAZA-PET hypoxia imaging was predictive of a tumor's response to evofosfamide.Conclusions: Our data demonstrate a novel means to target the CC-IC fraction by adding a HAP sequentially after conventional adjuvant therapy, as well as the use of FAZA-PET as a biomarker for hypoxia to identify tumors that will benefit most from this approach. Clin Cancer Res; 24(9); 2116-27. ©2018 AACR.

Radiotherapy Synergizes with the Hypoxia-Activated Prodrug Evofosfamide: In Vitro and In Vivo Studies

AIMS

Evofosfamide (TH-302) is a hypoxia-activated prodrug (HAP) that releases the DNA-damaging bromo-isophosphoramide mustard (Br-IPM) moiety selectively under hypoxic conditions. Since solid tumors are known to have hypoxic regions, HAPs in combination with chemotherapy or radiotherapy (XRT) will be beneficial. We tested the oxygen dependence of release kinetics of Br-IPM using electron paramagnetic resonance (EPR) with spin trapping by monitoring redox cycling of the nitroimidazole moiety of TH-302, and oxygen dependence of TH-302 on in vitro cytotoxicity at different levels of hypoxia was also examined. Two tumor implants (SCCVII and HT29) in mice were studied.

RESULTS

TH-302 fragmentation to release Br-IPM was noticed at oxygen levels <76 mmHg, which increased with higher levels of hypoxia. Enhanced cellular cytotoxicity was also observed at oxygen levels <76 mmHg. In vivo pO₂ imaging in the two tumor implants showed that the SCCVII tumor implant had higher level of hypoxia compared with the HT29 xenograft. TH-302 as a monotherapy in vivo showed modest effects in SCCVII implants and minimal effects in HT29 xenografts, whereas TH-302 in combination with ionizing radiation showed significant benefit in both tumor models.

INNOVATION

We examined the kinetics of redox cycling versus fragmentation of TH-302. The combination of oxygen-dependent XRT with TH-302 is effective even in tumors with significant hypoxia.

CONCLUSIONS

Imaging studies identifying the magnitude of hypoxia in tumors indicated that the responsiveness to TH-302 and the antitumor effect of TH-302 were enhanced by combining with XRT in both the TH-302-sensitive SCCVII tumor and -resistant HT29 tumor. Antioxid. Redox Signal. 28, 131-140.

Proteoglycan-targeting applied to hypoxia-activated prodrug therapy in chondrosarcoma: first proof-of-concept

Due to its abundant chondrogenic matrix and hypoxic tissue, chondrosarcoma is chemo- and radio-resistant. Our group has developed a proteoglycan targeting strategy by using a quaternary ammonium (QA) function as a carrier of DNA alkylating agents to chondrosarcoma environment. Here, we assessed the relevance of this strategy applied to hypoxia-activated prodrugs, by conjugating a QA to 2-nitroimidazole phosphoramidate. This derivative, named as 8-QA, was evaluated respectively to its non-QA equivalent and to a QA-conjugated but non-hypoxia activated. Firstly binding to aggrecan was confirmed from dissociation constant determined by Surface Plasmon Resonance. In vitro, in HEMC-SS chondrosarcoma cells cultured in monolayer and in spheroids, 8-QA showed higher cytotoxic activity in hypoxia versus normoxia, and led to a strong accumulation of cells in S phase and apoptosis. In vivo, a HEMC-SS xenograft model was implanted on SCID mice and characterized for hypoxia by photoacoustic imaging as well as proteoglycan content. When HEMC-SS bearing mice were given 8-QA at 47 μmol/kg according to a q4d x 6 schedule, a significant 62.1% inhibition of tumor growth was observed, without associated hematological side effects. Mechanistic studies of treated tumors highlighted decrease in mitotic index associated to increase in both p21 and p53S15 markers. Interestingly, 8-QA treatment induced an increase of DNA damages as measured by γH2AX predominantly found in pimonidazole-positive hypoxic areas. These preclinical results are the first to demonstrate the interest of addressing hypoxia-activated prodrugs selectively to proteoglycan of chondrogenic tumor tissue, as a promising therapeutic strategy.

Phase I study of pazopanib plus TH-302 in advanced solid tumors

PURPOSE

To define the maximum tolerated dose (MTD), recommended phase II dose (RPTD), and assess safety and tolerability for the combination of pazopanib plus TH-302, an investigational hypoxia-activated prodrug (HAP), in adult patients with advanced solid tumors.

METHODS

This was an open-label, non-randomized, single-center, phase I trial consisting 2 stages. Stage 1 was a standard "3 + 3" dose escalation design to determine safety and the RPTD for TH-302 plus pazopanib combination. Stage 2 was an expanded cohort to better describe the tolerability and toxicity profile at the MTD. Pazopanib was orally dosed at 800 mg daily on days 1-28 for all cohorts. TH-302 was administered intravenously on days 1, 8 and 15 of a 28-day cycle at doses of 340 mg/m² (cohort 1) or 480 mg/m² (cohort 2). Dose limiting toxicity (DLT) was assessed in the first 28-day cycle. Efficacy was assessed every 2 cycles.

RESULTS

Thirty patients were enrolled between December 2011 and September 2013. In the dose escalation stage, 7 patients were enrolled in the 340 mg/m² TH-302 cohort and 6 patients in the 480 mg/m² TH-302 cohort. Ten patients were evaluable for DLT. DLTs included grade 2 intolerable esophagitis (n = 1) in the 340 mg/m² TH-302 cohort, and grade 3 vaginal inflammation (n = 1) and grade 3 neutropenia with grade 3 thrombocytopenia (n = 1, same patient) in the 480 mg/m² TH-302 cohort. The 340 mg/m² TH-302 cohort was determined to be MTD and RPTD. The most common treatment-related adverse events were hematologic (anemia, neutropenia, and thrombocytopenia), nausea/vomiting, palmar-plantar erythrodysesthesia syndrome, constipation, fatigue, mucositis, anorexia, pain, and hypertension. Partial response (PR) was observed in 10% (n = 3) of patients, stable disease (SD) in 57% (n = 17), and progressive disease (PD) in 23% (n = 7). Due to toxicity, 3 patients were discontinued from study drug prior to first radiographic assessment but were included in these calculations. Disease control ≥6 months was observed in 37% of patients (n = 11).

CONCLUSIONS

The RPTD for this novel combination is pazopanib 800 mg daily on days 1-28 plus TH-302 340 mg/m² on days 1, 8 and 15 of each 28-day cycle. Preliminary activity was seen in treatment-refractory cancers and supports potential value of co-targeting tumor angiogenesis and tumor hypoxia.

Molecular Pathways: Hypoxia-Activated Prodrugs in Cancer Therapy

Hypoxia is a known feature of aggressive solid tumors as well as a critical hallmark of the niche in aggressive hematologic malignances. Hypoxia is associated with insufficient response to standard therapy, resulting in disease progression and curtailed patients' survival through maintenance of noncycling cancer stem-like cells. A better understanding of the mechanisms and signaling pathways induced by hypoxia is essential to overcoming these effects. Recent findings demonstrate that bone marrow in the setting of hematologic malignancies is highly hypoxic, and that progression of the disease is associated with expansion of hypoxic niches and stabilization of the oncogenic hypoxia-inducible factor-1alpha (HIF1α). Solid tumors have also been shown to harbor hypoxic areas, maintaining survival of cancer cells via the HIF1α pathway. Developing new strategies for targeting hypoxia has become a crucial approach in modern cancer therapy. The number of preclinical and clinical trials targeting low-oxygen tumor compartments or the hypoxic bone marrow niche via hypoxia-activated prodrugs is increasing. This review discusses the development of the hypoxia-activated prodrugs and their applicability in treating both hematologic malignancies and solid tumors. Clin Cancer Res; 23(10); 2382-90. ©2017 AACR.